As is known in the art, the current state of the art in Diesel Particulate Filter (DPF) assemblies are cylindrical structures such as that shown in FIG. 1 and described in described in U.S. Pat. No. 6,669,751. More particularly, the assembly includes inner rectangular cross section filter and outer filter having convex surfaces. Typically, the process used is to form the filters is by extrusion of material, typically silicon carbide, into elongated honeycomb structures having rectangular cross sections. The outer filters are also initially formed as rectangular structures and are further processed using a diamond-cutting tool to first cut along the diagonal of the rectangular section to separate the structure into two triangles, (i.e., a triangular prism shape) in order to facilitate a subsequent corner rounding process. Next, the DPF assembly is formed as shown in FIG. 1 having in the inner core a plurality of rectangular cross section shaped filters and the rounder corner, triangular shaped filters about a portion of the periphery of the assembly as described in the above-referenced U.S. Pat. No. 6,669,751.
This triangle cutting process is slow and costly due to the hardness and abrasive nature of the DPF material. The triangle cutting process is slow because it is done as an offline operation, requiring additional machinery and personnel to operate the machinery. Although suggested in U.S. Pat. No. 6,669,751, DPF manufacturers have experimented with extruding triangular sections, without commercial success. This is due to the fact that the material when extruded, i.e., prior to microwave drying, into triangles, more particularly into a triangular prism shape, lacks the rigidity to be handled and manipulated at its edges or corners.